INTRODUCTION 29 



cern us here, it is placed in the order Siphonaptera ; more 

 detailed specific characters apportion it to the genus Pulex 

 and finally to the species irritans. Certain orders have 

 been omitted from the classification, not necessarily be- 

 cause they are unimportant, but because their members 

 from one cause and another are not of great economic 

 import to man. 



An insect, unlike a man or a rabbit, does not, as a rule, 

 begin its separate existence as a miniature replica of an 

 adult, nor does it hatch from the egg in a form resembling 

 its parents, as in the case with the barnyard fowl ; it passes 

 through several changes, or metamorphoses, in the course 

 of its life. Taking the common house fly as an example 

 and studying its life-cycle, we find that the eggs give rise 

 to grubs or maggots, properly called larvae, and bearing no 

 manner of resemblance to the winged, six-legged mother 

 fly. Needless to say the larvae are small at first, but, as 

 they are voracious feeders, they grow rapidly, and their 

 skins, loosely fitting to begin with, are quickly filled out 

 and made a good fit ; then the larva moults, gets a new loose- 

 fitting coat, which is again similarly filled ; thus growth 

 takes place, though it is not so noticeable in the house fly 

 as in some of the lepidopterous larvae. When fully fed 

 the maggot changes into the chrysalis or pupa it is said 

 to pupate. No food is eaten, and to all appearances this is 

 an inert, resting stage, though, as a matter of fact, great 

 and important changes are taking place within the pupal 

 skin, for the insect is passing from the larval form to that 

 of the perfect insect. When pupation is complete the adult 

 fly emerges from its prison and is fully grown. It is a 

 popular error to imagine that flies grow, a remark that also 

 applies to butterflies and moths, bees, wasps, etc. Some- 

 times a newly emerged moth appears small by comparison 

 with the same individual after the lapse of an hour or two, 

 but this is simply due to the fact that the wings, moist and 

 crumpled at first, have had time to dry and expand. Such 



